Nowadays, cameras can be divided into two types according to how the films are used. One type is called as "whole frame" camera, and the other type as "half frame" camera. If we load a 36 exposure roll of film in a camera and we can only take 36 pictures, it is a "whole frame" camera, but if we load a 36 exposure roll of film and we can take 72 pictures, it is a "half frame" camera. The reason is that when the shutter release button of a whole frame camera is pressed, a whole frame of film will be exposed to light while in a "half frame" camera, only "one half" of a frame will be exposed to light. Therefore a "half frame" camera can take twice as many pictures as a "whole frame" camera. Of course, a "whole frame" camera can take wider and clearer pictures because its exposure area is a "whole frame". However, when an object to be photographed is too small or far away, areas around the frame would be unnecessary so as to waste some of the film. Under this situation, the most ideal and economic way is to take pictures with a "half frame" camera. Moreover, when we are taking pictures, we often find that, when the roll of film is nearly used up, there are still several valuable pictures not yet taken, but there is insufficient film left. Under such situation it would be convenient if we could change a "whole frame" camera to a "half frame" camera in order to take the desired pictures. It has previously been proposed to provide devices for adjusting the exposure area or to adjust photographing but such devices have tended to be complicated and inefficient.
One such device proposed in U.S. Pat. No. 2,247,104 adjusts the exposure area of a film by using a roll and a string to pull a screen to move toward the film horizontally so that the area of exposure can be appropriately shielded. This device is very complicated, cannot ensure the film length which has been wound, and can not be easily operated.
Another device has been proposed in U.S. Pat. No. 2,295,801 which uses a slide to adjust a mask plate to shield the dimensions of the viewfinder and adjust the winding length of the film simultaneously by means of a gear set. Another separate operation makes the opening rotate 90 degrees to change the exposure area.
A further device has been proposed in U.S. Pat. No. 2,522,387, in which the body of the camera can be moved from two end sides toward the centre to change the width of the camera body such that the exposure area and the viewfinder dimensions are adjusted.
All the devices described above possess a complicated structure and cannot be manufactured easily. Therefore, my former U.S. pending patent is identified with Ser. No. 706,291 providing a device which can change dimensions quickly and be operated easily.